The construction "be of + noun" is virtually the same as "be + adjective" except it sounds more formal. You can think of it as to be of a certain class or of a certain type. The book is of interest = The book is interesting. (The book is typified/classified as interesting) Can I be of any help? = Can I be helpful? (Can I be classified as helpful) *note that this is a set phrase. Nobody would ever say "Can I be helpful?" in this context The ordinary people were of Saxon blood = The ordinary people were Saxon (They were classified as Saxon)

Be of: possess intrinsically; give rise to. Basically, it IS or HAS or GENERATES whatever it is "of". Examples: ‘this work is of great interest and value’ (it's interesting and valuable) ‘The story was of particular interest to me as a New Zealander living in Australia.’ (it's interesting) ‘Listen and make the other person feel that what he or she is saying is of interest to you.’ (is interesting) ‘The school has a number of buildings listed as being of historic interest.’ (the history is interesting) ‘Warrington council has recognised the building as being of historical interest.’ (the history is interesting) ‘Why people read what they read and watch what they watch has recently been of interest to me.’ (it's interesting) ‘The software will be of interest to schools and museums, as well as town planners.’ ‘The rise in the rate of suicide amongst young people is of constant concern to our agency.’ ‘They were getting historic items that they felt were of too great an importance to sell on and should be on public display.’ ‘Sgt Brown added the cars involved were of little value with only one new vehicle being seized over the past six months.’ ‘Many of the calls were of a difficult nature from distressed families with moving reports of missing people.’